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SUMMARY
This article provides an overview of the
A-V Search Hysteresis (AVSH) feature
available in many Boston Scientific
pacemakers. This overview includes:
ƒ How AVSH works
ƒ How AVSH can encourage AV
conduction and help reduce RV
pacing
ƒ Parameters associated with AVSH
ƒ Considerations for programming
an extended AV Delay
CRM PRODUCTS REFERENCED
The following are trademarks of Cardiac Pacemakers Inc.,
a Boston Scientific company: ALTRUA, INSIGNIA I Plus/,
INSIGNIA AVT, INSIGNIA Ultra, PULSAR MAX II,
PULSAR MAX, PULSAR.
Products referenced herein may not be approved in all
geographies. For comprehensive information regarding
device operation, please reference the appropriate product
labeling.
CRM CONTACT INFORMATION
United States
www.bostonscientific.com
A-V Search Hysteresis (AVSH) is a feature available in dual-chamber pacemakers
designed to allow intrinsic conduction that might otherwise be masked by continuous
pacing (i.e., pacing at an AV Delay that is shorter than the patient’s P-R interval). AVSH
may be useful for patients with exercise-dependent or intermittent AV nodal block. During
normal AV nodal function, this feature temporarily allows intrinsic AV conduction to exceed
the programmed AV Delay, thereby encouraging intrinsic AV conduction and reducing
ventricular pacing. This may improve hemodynamic performance and increase device
longevity due to a reduced number of ventricular paces. Reducing the amount of RV
pacing in pacemaker patients: 1) moderately reduces the risk of developing persistent atrial
fibrillation,1 and 2) may reduce the progression to heart failure.2
How AVSH Works
Programmable parameters associated with AV Delay and AVSH are described in
Table 1. When the AVSH feature is enabled, the AV Delay (either fixed or Dynamic) is
periodically lengthened for up to 8 consecutive cardiac cycles to search for intrinsic P-R
intervals that are longer than the programmed AV Delay. The AV Delay is lengthened
by the programmed percentage AV Increase, and once increased, will remain extended
as long as ventricular sensing is occurring. The pacemaker will revert to the
programmed paced AV Delay following the first ventricular pace at the Hysteresis AV
Delay, or when the 8-cycle search window expires without sensing intrinsic ventricular
activity.
Figure 1 illustrates the operation of AVSH. In this example, the device meets the
programmed AVSH Search Interval criteria by consecutively pacing in the ventricle for
32 cycles. At this point, the AV Delay is lengthened by 100% (the programmed AV
Increase) in search of intrinsic P-R activity. During the 1st cycle, the intrinsic P-R
interval is longer than the Hysteresis AV Delay of 400 ms, so the ventricle remains
paced. During cycles 2-17, because the intrinsic P-R interval is less than the
Hysteresis AV Delay, ventricular pacing is inhibited to allow for intrinsic conduction.
Pacing resumes on the 18th cycle because the P-R interval is once again longer than
the Hysteresis AV Delay. At this point, the AV Delay returns to its programmed value,
and a new Search Interval count begins.
Technical Services – U.S.
LATITUDE Clinician Support – U.S.
1.800.CARDIAC (227.3422)
+1.651.582.4000
[email protected]
[email protected]
Patient Services
1.866.484.3268
Continued
operation at
extended AV
Delay and
inhibited VP
Search begins
32
31st cycle
1
2
3
Return to
programmed AV
Delay and new
Search Interval
count begins
VP to avoid
dropped beat
17
1
18
International
www.bostonscientific-international.com
Technical Services – Europe
+32 2 416 7222
[email protected]
International LATITUDE Customer Support
www.latitude.bostonscientific-international.com
[email protected]
AV Delay
200 ms
VP
AV Delay
200 ms
VP
AV Delay
400 ms
VP
PR Interval
350 ms
VS
AV Delay
400 ms
VS
VS
VP
AV Delay
200 ms
VP
Figure 1. Example of A-V Search Hysteresis operation.
November 30, 2009
©2009 Boston Scientific Corporation or its affiliates. All rights reserved.
002-1198, Rev. A
Page 1 of 3
Activating AVSH
Although significant ventricular pacing would be expected for patients with more severe AV block, AVSH may provide an
opportunity to encourage AV conduction and thereby reduce ventricular pacing for some patients with 1st degree or 2nd
degree AV block.
Figure 2 displays the ZOOM® LATITUDE® programmer screen used to activate AVSH in an ALTRUA® pacemaker.
With this programming, the device will allow the AV Delay to reach, but never exceed the maximum of 400 ms.
Current programmed AV Delay parameters
Current programmed AVSH parameters,
including how often a search is conducted
and the amount AV Delay will be lengthened
during the search
Figure 2. ALTRUA Brady Parameters programmer screen.
An ALTRUA Counters report is shown in Figure 3. Since the previous follow-up visit, the device has paced in the ventricle
40% of the time, and has conducted 35 successful searches out of 39 search attempts.
40% RV Pacing
35 successful AVSH searches
Figure 3. Counters report from an ALTRUA
pacemaker with AVSH On.*
________________________________
* Individual symptoms, situations, circumstances, and results may vary.
November 30, 2009
©2009 Boston Scientific Corporation or its affiliates. All rights reserved.
002-1198, Rev. A
Page 2 of 3
Table 1. Programmable Parameters Associated with A-V Search Hysteresis
Programmable
Parameters of
Interest
AV Delay
Description
Period from the beginning of an atrial event (either
intrinsic or paced) to the paced ventricular event
Programmable Values
10–300 ms in 10 ms increments for ALTRUA
20/ 40 series, INSIGNIA I Plus/ AVT/Ultra,
PULSAR MAX II, PULSAR MAX, and
PULSAR pacemakers
10–400 ms in 10 ms increments for ALTRUA
50/60 series pacemakers
Nominal = 150 ms
Off, On
Dynamic AV Delay
Maximum Delay
Mimics normal AV nodal function by adjusting AV
Delay in response to rate changes
Longest Dynamic AV Delay allowed; will be applied
at the lower rate limit
¾
Nominal = On (ALTRUA™, and
INSIGNIA® pacemakers)
¾
Nominal = Off ( PULSAR® MAX II,
PULSAR MAX, and PULSAR
pacemakers)
¾
20–300 ms in 10 ms increments for
ALTRUA 20/40 series, INSIGNIA I Plus/
AVT/Ultra, PULSAR MAX II, PULSAR
MAX, and PULSAR pacemakers
¾
20–400 ms in 10 ms increments for
ALTRUA 50/60 series pacemakers
Nominal = 150 ms
Minimum Delay
Shortest Dynamic AV Delay allowed; will be applied
at the maximum tracking rate
AV Search Interval
Activates AV Search Hysteresis and controls how
often an AV search (up to 8 cycles long) will be
conducted
AV Increase
Determines how much the AV Delay (either
standard or dynamic) will be lengthened during a
search cycle.
10–290 ms in 10 ms increments
Nominal = 80 ms
OFF, 32, 64, 128, 256, 512, 1024 cycles
Nominal = Off
10%–100% in 10% increments
Nominal = 30%
Considerations for Extending AV Delay
While the use of AVSH may be beneficial in reducing unnecessary RV pacing for some patients, long AV intervals (≥ 250
ms) should be used with caution. Physicians should evaluate the patient and weigh the potential benefit of promoting
intrinsic conduction against the potential risk of hemodynamic compromise, such as pacemaker syndrome and diastolic
mitral regurgitation.
1
Sweeney, MO, Bank, AJ, Nsah, E, et. al. Minimizing ventricular pacing to reduce atrial fibrillation in sinus node disease. N Engl J Med. 2007; 357: 10001008.
2
Sweeney, MO, Hellkamp AS, Ellenbogen KA, et. al. Adverse effect of ventricular pacing on heart failure and atrial fibrillation among patients with normal
baseline QRS duration in a clinical trial of pacemaker therapy for sinus node dysfunction. Circulation. 2003;107: 2932-2937.
November 30, 2009
©2009 Boston Scientific Corporation or its affiliates. All rights reserved.
002-1198, Rev. A
Page 3 of 3